Maternal folate polymorphisms and the etiology of human nondisjunction

Attempts to identify genetic contributors to human meiotic nondisjunction have met with little, if any, success. Thus, recent reports linking Down syndrome to maternal polymorphisms at either of two folate metabolism enzymes, methylenetetrahydrofolate reductase (MTHFR) and methionine synthase reductase (MTRR), have generated considerable interest. In the present report, we asked whether variation at MTHFR (677C-->T) or MTRR (66A-->G) might be associated with human trisomies other than trisomy 21. We analyzed maternal polymorphisms at MTHFR and MTRR in 93 cases of sex-chromosome trisomy, 44 cases of trisomy 18, and 158 cases of autosomal trisomies 2, 7, 10, 13, 14, 15, 16, 18, or 22, and compared the distributions of genotypes to those of control populations. We observed a significant increase in the MTHFR polymorphism in mothers of trisomy 18 conceptuses but were unable to identify any other significant associations. Overall, our observations suggest that, at least for the sex chromosomes and for a combined set of autosomal trisomies, polymorphisms in the folate pathway are not a significant contributor to human meiotic nondisjunction.

Steroid sulfatase activity in leukocytes: a comparative study in 45,X; 46,Xi(Xq) and carriers of steroid sulfatase deficiency

The enzyme steroid sulfatase (STS) hydrolyses 3-beta-hydroxysteroid sulfates. The female-male STS activity ratio is 1.04-1.7:1 in several cell lines in adults and reaches 2:1 in prepubertal subjects. In fibroblasts, STS values in X-chromosome abnormalities show a partial positive correlation according to the number of X-chromosomes. X-linked ichthyosis (XLI) carriers, with only one copy of the STS gene, present lower STS levels than normal controls. This study analyzes the STS activity in leukocytes of 46,Xi(Xq); 45,X; XLI carriers and normal controls using 7-[3H]-dehydroepiandrosterone sulfate as substrate. X-monosomy (1.07 +/- 0.18 pmol/mg protein/h), Xq isochromosome (1.02 +/- 0.12 pmol/mg protein/h) and normal females (1.03 +/- 0.11 pmol/mg protein/h) had similar STS values (p > 0.05). XLI-carriers and males showed the lowest STS levels (0.34 +/- 0.04 pmol/mg protein/h, p < 0.001 and 0.82 +/- 0.14 pmol/mg protein/h, p < 0.05, respectively). Female-male STS activity ratio in leukocytes was 1.3:1. These data indicate that a complex mechanism regulates the STS expression depending on each type of cell line.

Phospholipase D activity is altered in X-linked adrenoleukodystrophy heterozygous carriers, but not in hemizygous patients

Abnormalities in levels of choline and its metabolites have been reported in the lesions of brains of X-linked adrenoleukodystrophy (X-ALD) patients. We have examined the turnover of the major choline-containing phospholipid, phosphatidylcholine (PtdCho), in fibroblasts from hemizygous X-ALD, heterozygous X-ALD, Zellweger syndrome (ZW), and male and female control individuals to assess possible alterations in PtdCho metabolism mediated by activation of protein kinase C (PKC). Hydrolysis of PtdCho by phospholipase D (PLD) and resynthesis of PtdCho from labeled choline were stimulated 2- to 4-fold by PKC activation with the phorbol ester, 4beta-12-O-tetradecanoylphorbol-13-acetate (beta-TPA), in all cells except those from heterozygous X-ALD individuals. No differences in quantity or intracellular distribution of PKC activity, PKC isoforms by Western blot analysis, or of the PKC substrate, myristoylated alanine-rich C kinase substrate (MARCKS), were apparent in any of the cells. Thus, altered PtdCho metabolism was not directly linked to either of these inherited defects that result in abnormal peroxisomal functions. Further, altered responsiveness of PLD in X-ALD heterozygotes was independent of changes in PKC and MARCKS.

Mutations in the kinase Rsk-2 associated with Coffin-Lowry syndrome

The Coffin-Lowry syndrome (CLS), an X-linked disorder, is characterized by severe psychomotor retardation, facial and digital dysmorphisms, and progressive skeletal deformations. Genetic linkage analysis mapped the CLS locus to an interval of 2-3 megabases at Xp22.2. The gene coding for Rsk-2, a member of the growth-factor-regulated protein kinases, maps within the candidate interval, and was tested as a candidate gene for CLS. Initial screening for mutations in the gene for Rsk-2 in 76 unrelated CLS patients revealed one intragenic deletion, a nonsense, two splice site, and two missense mutations. The two missenses affect sites critical for the function of Rsk-2. The mutated Rsk-2 proteins were found to be inactive in a S6 kinase assay. These findings provide direct evidence that abnormalities in the MAPK/RSK signalling pathway cause Coffin-Lowry syndrome.

Deletion of the distal short arm of the X chromosome (Xp) in a patient with short stature, chondrodysplasia punctata, and X-linked ichthyosis due to steroid sulfatase deficiency

We observed a boy with short stature, chondrodysplasia punctata, ichthyosis, and a terminal deletion of Xp. Steroid sulfatase deficiency was demonstrated in the patient's fibroblasts. Molecular analysis showed a deletion of the entire steroid sulfatase gene. This case represents another example of a contiguous gene syndrome in which the co-deletion of adjacent genes on a chromosome is responsible for a complex phenotype.

Plasma amine oxidase activities in Norrie disease patients with an X-chromosomal deletion affecting monoamine oxidase

Two individuals with an X-chromosomal deletion were recently found to lack the genes encoding monoamine oxidase type A (MAO-A) and MAO-B. This abnormality was associated with almost total (90%) reductions in the oxidatively deaminated urinary metabolites of the MAO-A substrate, norepinephrine, and with marked (100-fold) increases in an MAO-B substrate, phenylethylamine, confirming systemic functional consequences of the genetic enzyme deficiency. However, urinary concentrations of the deaminated metabolites of dopamine and serotonin (5-HT) were essentially normal. To investigate other deaminating systems besides MAO-A and MAO-B that might produce these metabolites of dopamine and 5-HT, we examined plasma amine oxidase (AO) activity in these two patients and two additional patients with the same X-chromosomal deletion. Normal plasma AO activity was found in all four Norrie disease-deletion patients, in four patients with classic Norrie disease without a chromosomal deletion, and in family members of patients from both groups. Marked plasma amine metabolite abnormalities and essentially absent platelet MAO-B activity were found in all four Norrie disease-deletion patients, but in none of the other subjects in the two comparison groups. These results indicate that plasma AO is encoded by gene(s) independent of those for MAO-A and MAO-B, and raise the possibility that plasma AO, and perhaps the closely related tissue AO, benzylamine oxidase, as well as other atypical AOs or MAOs encoded independently from MAO-A and MAO-B may contribute to the oxidative deamination of dopamine and 5-HT in humans.

Use of X chromosome inactivation analysis to establish carrier status for X-linked severe combined immunodeficiency

Analysis of X chromosome inactivation in T-lymphocyte DNA from two obligate carriers of X-linked severe combined immunodeficiency showed a non-random pattern. This method was then used to establish carrier status in at-risk females in X-linked pedigrees. It was further used to differentiate between X-linked and autosomal recessive inheritance of the disease when the mode of inheritance was not clear from the pedigree. In addition, a mother of a boy affected by the sporadic form of the disease was found to have non-random X inactivation in her T lymphocytes and she is therefore a carrier of the X-linked disease.

Expression of two G-6-PD genes in an XX phenotypic male

The glucose-6-phosphate dehydrogenase (G-6-PD) gene is located on the X-chromosome. Normal males have a single gene and produce a single G-6-PD type, while normal XX females may be heterozygotes for two different G-6-PD genes. We report the case of a phenotypic male who was found to be heterozygous for two G-6-PD enzymes. Cytogenetic analysis showed that he was a 46,XX male.

Lymphocyte phosphorylase kinase activities in the sex-linked form of liver phosphorylase kinase deficiency

Lymphocyte phosphorylase kinase activities were measured in normal controls and in patients with the sex-linked form of liver phosphorylase kinase deficiency. The reaction due to phosphorylase kinase activity in normal lymphocytes (2.7 X 10(6) in the reaction tube) was found to be linear within 20-60 min at 30 degrees C. The reaction was directly proportional to the concentration of lymphocytes within 1.5 X 10(6)-9.0 X 10(6), at 30 degrees C for 60 min. The phosphorylase kinase activity in normal lymphocytes, which were pre-incubated at 50 degrees C or 95 degrees C for 1 min, decreased to 60% at 50 degrees C and 10% at 95 degrees C of that after pre-incubation at 0 degree C for 1 min. The activity of normal controls was 125 +/- 23.5 U/10(10) lymphocytes. Those of the patients with liver phosphorylase kinase deficiency due to the sex-linked form were 43.5 U in case 1, 54.5 U in case 2, and 51.3 U in case 3, respectively and those of the mothers were within the normal range. These results suggest that phosphorylase kinase in lymphocytes might be form intermediate between liver and muscle phosphorylase kinase.

Placental steroid sulphatase deficiency

Low maternal plasma and urinary oestrogen concentrations in pregnancy are usually indicative of fetal problems, either placental insufficiency or fetal adrenal hypoplasia. Paediatricians, however, should follow obstetricians in becoming increasingly aware that deficiency of placental steroid sulphatase activity, a condition related to X linked ichthyosis, may produce the same abnormalities.

A comparative study on steroid sulfatase and arylsulfatase C in fibroblast clones from 45,X/47,XXX and 69,XXY

Steroid sulfatase (STS) and arylsulfatase C ( ARSC ) were studied in fibroblast clones from a 45,X/47,XXX mosaic and from a 69,XXY triploidy with one or two active X chromosomes. The comparison of the 47,XXX with 45,X clones showed an incomplete gene dosage effect (1.8 for STS and 2.0 for ARSC ). This was not the case for the triploid clones with different X-inactivation patterns. These results confirm previous reports on the non-inactivation of the STS gene, and establish X linkage and non-inactivation for the ARSC gene as well.

Evidence for a dosage effect at the X-linked steroid sulfatase locus in human tissues

Steroid sulfatase (STS) is an X-linked enzyme whose locus escapes X inactivation in human somatic cells. STS activity was determined in human fibroblasts varying in X-chromosome number from one to four. Greater STS activity was detected in 2X cell strains when compared to 1X cell strains; however, increased STS activity was not found in 3 and 4X strains as compared with the 2X strains. Greater STS activity was also observed in female hair follicles when compared with male hair follicles. These data provide evidence of a gene dosage effect at the STS locus in human tissues.

Abnormal regulation of renal 25-hydroxyvitamin D-1 alpha-hydroxylase activity in the X-linked hypophosphatemic mouse

Abnormal vitamin D metabolism has been suspected in patients with X-linked hypophosphatemic rickets (XLH) and X-linked hypophosphatemic mice (Hyp-mice), the murine homologue of the human disease. We compared 25(OH)D-1 alpha-hydroxylase activity in the Hyp-mouse kidney to that in normal and phosphate-depleted mouse kidney. Weanling normal and Hyp-mice were fed a 0.6% phosphorus diet; phosphate-depleted mice received a 0.02% phosphorus diet. At 8-10 wk of age the serum phosphorus values in Hyp (3.35 +/- 0.12 mg/dl) and phosphate-depleted mice (3.83 +/- 0.56) were not significantly different. Despite the similar magnitude of phosphate depletion, however, the maximum levels of 25(OH)D-1 alpha-hydroxylase activity were disparate: phosphate-depleted mouse kidney had profoundly increased activity compared to normal (17.04 +/- .104 vs. 4.96 +/- 0.23 fmol 1,25(OH)2D3 produced/mg kidney per min) while Hyp-mouse kidney had a fourfold lesser increment (8.18 +/- 0.62). These data indicate that phosphate depletion is a potent stimulus of 25(OH)D-1 alpha-hydroxylase activity in the (C57BL6J) mouse. Moreover, the results show that abnormal regulation of 25(OH)D-1 alpha-hydroxylase activity is manifest in the Hyp-mouse.

X-chromosome activity in the germ cells of sex-reversed mouse embryos

Germ cells were isolated from XX ovaries and XY and XX Sex-reversed (Sxr/+) testes of mouse embryos 14-16 days post coitum, and the activity of an X-chromosome-coded enzyme, hypoxanthine phosphoribosyl transferase (HPRT), relative to an autosomal one, adenine phosphoribosyl transferase was determined. The ratio of enzyme activities in XX Sxr/+ prospermatogonia was significantly higher than that in XY prospermatogonia, up to 2-fold, suggesting that the silent X chromosome is reactivated in XX male germ cells before birth, as it is in female germ cells. The ratio was several times higher still in XX oocytes than in XX prospermatogonia, confirming that the increase in HPRT activity reported in oocytes is only partly due to an X-chromosome dosage effect.

Fragile X syndrome: search for phenotypic manifestations at loci for hypoxanthine phosphoribosyltransferase and glucose-6-phosphate dehydrogenase

The subjects of this study were individuals with the form of X-linked mental retardation that is associated with the presence of a cytologically variant X chromosome having a secondary constriction or "fragile site" at Xq 27-28 (Fra X). Studies were carried out to test the hypothesis that deletions or modifications at neighboring loci occur as a consequence of events at the fragile site. Skin fibroblasts and peripheral blood lymphocytes from affected males were analyzed with respect to the expression of two X-lined enzymes: glucose-6-phosphate dehydrogenase (G6PD) and hypoxanthine phosphoribosyltransferase (HPRT); loci for these enzymes are known to be located in the region of the fragile site. Although the number of cells resistant to thioguanine (HPRT-deficient) obtained from some cultures from one Fra X male and blood cells of another was greater than expected, the frequency of these cells was not increased in cultures from other Fra X males. Furthermore, our results indicate that the G6PD activity and electrophoretic mobility in Fra X males is similar to that in normal cells, thus providing no evidence for the loss of the long-arm telomere in the fragile X syndrome.

Activity of steroid sulfatase in fibroblasts with numerical and structural X chromosome aberrations

In cultured fibroblasts of patients with numerical and structural X chromosome aberrations the activity of steroid sulfatase (STS) is correlated with the number of functional STS gene copies. While normally, this X-linked gene is not inactivated, our data suggest that it may be subject to inactivation when carried on a structurally altered X-chromosome. Similar inactivation patterns have been reported earlier for the Xg locus which, like STS, is located on the distal portion of Xp.

X-linked recessive (Duchenne) muscular dystrophy (DMD) and purine metabolism: effects of oral allopurinol and adenylate

Data are presented which suggest that Duchenne muscular dystrophy (DMD) may have some origin in a severe deficiency of total muscle adenine nucleotides. Using double-blind techniques, this possibility was tested in 16 DMD patients by giving oral allopurinol, a synthetic inhibitor of the purine catabolic enzyme xanthine oxidase. Sublingual procaine adenylate was also briefly tested. Instances of clinical improvement quickly occurred which were statistically significant; they were accompanied by a significant increase in physical strength. These improvements have been maintained for more than 6 mo by administration of a small amount of allopurinol daily. Procaine adenylate had little effect. These results support the above view of DMD and seem to indicate that existing purines, retained and recycled after allopurinol, can sustain such improvement, and that additional adenylate is unnecessary.

Carrier detection and genetic counselling in Duchenne muscular dystrophy: a follow-up study

Assay of serum creatine kinase activity is useful in the detection of carriers of the X-linked gene for Duchenne muscular dystrophy (DMD). For genetic counselling this assay has been used in conjunction with pedigree analysis to improve estimates of the risk that a female relative of a DMD patient is a carrier. To measure the impact of the program, follow-up information was obtained from women who had received genetic counselling for DMD. Their responses showed that the risk of producing an affected son had been a major factor in their attitude toward family planning, and their reproductive performance correlated inversely with their genetic risk. The decision by the majority of proven carriers to prevent the birth of further male offspring was reflected in a recent decline in the frequency of a known family history of DMD among newly ascertained cases.

Evidence for two active X chromosomes in a human XXY triploid

A human XXY chromatin negative triploid culture has been found to have both the A and B isozymes of glucose-6-phosphate dehydrogenase, as well as an intermediately migrating AB (hybrid) band. This finding indicates that the cells in this culture each possess 2 active X chromosomes. Possible mechanisms producing the abnormalities seen in this disorder are presented and discussed.

Mammalian oocytes: X chromosome activity

The glucose-6-phosphate dehydrogenase and lactate dehydrogenase contents of oocytes from XO and XX female mice have been measured. The activity of the former in the oocytes of XO mice is half of that in the oocytes of XX mice, whereas the lactate dehydrogenase activities in the two groups of ova are the same. These results indicate that glucose-6-phosphate dehydrogenase from a mouse oocyte is an X-linked enzyme, that its synthesis occurs in the oocyte and is dosage dependent, and that inactivation of the X chromosome does not occur in the mouse oocyte.